Organic polymer materials which have large second order non-linear optical (NLO) response are of interest for optical applications including communications, data storage, and computing. Important applications include waveguides, interconnects, switches, and the like. Their advantages over the conventionally employed inorganic materials, e.g. LiNbO.sub.3, in such applications include fast response time, large electro-optical response over a wide frequency range, low dielectric constant, compatibility with silicon wafer technology and others. However, NLO active polymers known from the prior art suffer from lack of long term stability under working temperature conditions, which limits their practical utility. The present invention provides fluorene-based compounds which are highly NLO active through their unsymmetrical substitution at the aromatic rings. Those which have functional groups which permit polymerization can be used for making NLO active polymers with high glass transition temperature; all can be used as additives in host-guest polymer systems. Some can be grown into non-centrosymmetric crystals.